A hybrid vehicle may provide regenerative and friction braking to slow the hybrid vehicle. An electric machine is applied during regenerative braking to slow the hybrid vehicle and convert the hybrid vehicle's kinetic energy into electrical energy. Friction brakes may be utilized when the hybrid vehicle's regenerative braking capacity alone is insufficient to stop the hybrid vehicle. However, utilizing friction brakes may waste the hybrid vehicle's kinetic energy by converting the hybrid vehicle's kinetic energy into heat instead of electrical energy. Therefore, it may be desirable to activate and utilize regenerative braking whenever it may be desirable to slow the hybrid vehicle. Nevertheless, sometimes a hybrid vehicle may be presented with few opportunities to apply regenerative braking. Further, even if regenerative braking may be applied, driving conditions may limit use of regenerative braking to reduce the possibility of wheel slip. Consequently, it may be desirable to develop methods and systems that may improve a hybrid vehicle's capacity to reduce vehicle speed and recharge vehicle batteries via regenerative braking.
The inventors herein have recognized the above-mentioned issues and have developed a driveline method, comprising: adjusting a clutch torque of a differential's clutch in response to a difference between a second wheel braking torque and the first wheel threshold braking torque; and adjusting an electric machine regenerative torque in response to a first wheel braking torque and the first wheel braking torque and the clutch torque.
By adjusting a torque of an electrically controlled differential and electric machine regenerative torque, it may be possible to increase efficiency of converting a vehicle's kinetic energy into electrical energy even when opportunities to utilize regenerative braking may be low. In particular, the torque of the electrically controlled differential may be adjusted while a vehicle is negotiating a turn so that transfer of torque from vehicle wheels to an electric machine may be maximized without inducing wheel locking. Further, in examples where an axle controls torque of the clutch in a differential, electric machine regenerative torque may be adjusted in response to the torque of the clutch in the differential.
The present description may provide several advantages. In particular, the approach may improve efficiency of converting a vehicle's kinetic energy into electrical energy. Further, the approach may improve driving dynamics. In addition, the approach may provide benefits during vehicle cornering and while a vehicle is operating on a road that has different coefficients of friction for a first drive wheel and a second drive wheel.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.